1. Field of the Invention
The present invention relates to a reflection type liquid crystal display apparatus using an active matrix type driving system, a substrate for a reflection type liquid crystal, and a liquid crystal projector system. More particularly, the present invention relates to a reflection type liquid crystal display apparatus including a semiconductor substrate having a plurality of pixels disposed in a matrix thereon, each pixel including a switching element, a capacitor and an reflective electrode, and a light transmitting substrate having a light transmitting electrode formed thereon the reflective electrode facing the light transmitting electrode, a substrate for a reflection type liquid crystal display apparatus using a semiconductor substrate, and a liquid crystal projector system.
2. Description of the Related Art
In recent years, liquid crystal display apparatuses are widely spread for applications from compact display apparatuses to terminals of so called OA equipment (automated office equipment), in particular, in the office equipment, projection type liquid crystal display apparatuses where an image is projected on a large screen, are actively used.
With regard to such kinds of projection type liquid crystal display apparatus, there are two main types: a transmission type liquid crystal display apparatus and a reflection type liquid crystal display apparatus. In the former transmission type liquid crystal display apparatus, there is a problem in that, due to a switching element (transistor), a capacitor and a wiring provided to each of pixels, the transmission region of a pixel for transmitting a light reduces aperture ratio.
In the reflection type liquid crystal display apparatus, any region except for a region for insulating and isolating an pixel electrode for reflection of each pixel (hereinafter referred to as a reflective electrode) can be made as a reflective electrode. In addition, since a switching element, a capacitor, and a wiring which are required for driving an active matrix, can be arranged below the reflective electrode, the reflection type liquid crystal display apparatus has many advantages as compared to the transmitting type liquid crystal display apparatus, in compacting a liquid crystal display panel, high definition, and high brightness.
In general, in the above-mentioned reflection type liquid crystal display apparatus, a plurality of reflective electrodes connected to switching elements such as MOS transistors are arranged in a matrix on a semiconductor substrate (Si substrate). Moreover, the reflection type liquid crystal display apparatus has a configuration where a light transmitting common electrode facing to the plurality of reflective electrodes and to be common to all pixels, is placed, and further a liquid crystal is injected between the reflective electrodes of the semiconductor substrate and the common electrode. In such a reflection type liquid crystal display apparatus, by incidenting a light from the common electrode side and by corresponding the potential difference between the common electrode and the reflective electrode to an image signal and by controlling the orientation of the liquid crystal in each pixel, a reflected light is modulated.
In recent years, since high definition for the liquid crystal display apparatus has been required, and the reflection type liquid crystal display apparatus projects and displays an image on a large screen, needs of high definition pixels are big. Accordingly, if a high definition liquid crystal display apparatus is made by easygoing way of thinking, the chip size of the semiconductor substrate tends to be larger and larger. However, the large chip size directly leads to cost increase. Therefore, it is desirable to make the chip size as small as possible, and for this purpose, miniaturization of the pixel size is required.
In general, in consideration of reliability such as seizure, a voltage applied to the liquid crystal of a liquid crystal display apparatus is subjected to so called inversion driving where the voltage applied to the liquid crystal apparatus is reversed, for example, each frame. Therefore, a supply power voltage required to drive the liquid crystal display apparatus is required to be an order of 15 V (or more). In other words, this means that the withstanding voltages of pixels formed on a semiconductor substrate and elements (transistors and capacitors) constituting a periphery drive circuit, are required to be an order of 15 V (or more).
However, in order to ensure the withstanding voltage of each element, some amount of element size or element isolation space is required. In other words, although a small pixel size is required, from the design rule of element formation (definition of sizes such as a pixel size and element isolation space required when a device is formed), the size cannot be caused to be small. Accordingly, in order to cause the element size to be small, the capacitor of each pixel tends to be small.
However, since, if the capacitor is caused to be small, the quantity of an image is reduced and the image is susceptible to cross-talk from a signal line due to voltage drop caused by leakage from the capacitor end, the quantity of an output image will be reduced. Therefore, it is desirable for the capacitor to be as large as possible.
In order to cause the capacitor of the pixel to be large, the size of a capacitor electrode in the pixel should be as large as possible.
FIG. 9 is an example of a conventional pixel layout, and FIG. 10 is a cross-sectional view along line 10-10 of FIG. 9. This configuration is disclosed in Japanese Patent Application Laid-Open No. 2004-309681.
As a semiconductor substrate to be a base, a p-type mono-crystal silicon substrate (hereinafter, referred to as a p-type Si substrate) is used, and on the substrate a gate line 201 formed with polysilicon is wired in a horizontal direction. Then, a part of the gate wiring is separated and acts as a gate of NMOS transistor to be a switching element. A source region 202 of a switching transistor to be a switching element is connected to a signal line 204 formed with a first metal layer via a source contact 203. A drain region 205 of the switching transistor is connected to a drain wiring 207 formed with the first metal layer via a drain contact 206. The drain wiring 207 is connected to a capacitor electrode 209 formed with polysilicon via a contact 208.
The counter electrode of the capacitor electrode 209 acts as an N+type diffusion layer formed on a silicon substrate by means of ion implantation, and the diffusion layer acts as a common electrode 210 being common to whole pixels. Moreover, an insulating film between the capacitor electrode 209 and the common electrode 210 is generally formed by means of the same process as the process of a gate oxide film forming NMOS transistor.
In FIG. 10, a p-type Si substrate 211 is illustrated, where, in the left side, an NMOS transistor acting as a switching element is formed between field oxide films 212a and 212b. A gate electrode (a part of the gate wiring) 201 of the NMOS transistor, a source region 202, and a drain region 205 are illustrated.
The source region 202 is connected to the signal line 204 formed with the first metal layer via the source contact 203. The drain region 205 is connected to the drain wiring 207 formed with the first metal layer via the drain contact 206. The drain wiring 207 is connected to the capacitor electrode 209 via the contact 208, and further connected to the reflective electrode 214 formed with a third metal layer via a through hole 213. Moreover, since the common electrode (Vcom electrode) 210 being the counter electrode of the capacitor electrode 209 is formed with an N+type diffusion layer, both sides thereof, similar to the NMOS transistor, are formed between the field oxide films 212b and 212c. Moreover, between the first metal layer and the reflective electrode 214, in order to shielding incident light from the gap between itself and a neighboring reflective electrode, a light shielding layer 215 formed with the second metal layer is placed. In addition, in the light shielding layer 215, at a position through which the through hole 213 is passed, in order to obtain electrical insulation, a hole is opened. In addition, in order to obtain the capacitor of the pixel as much as possible, a fixed potential is given to the shielding layer 215.
Although a liquid crystal layer 217 is not illustrated, it is inserted between liquid crystal common electrodes 216 at a predetermined gap, which are formed with a light transmitting substrate acting as a counter electrode of the reflective electrode 214 after a protection film is coated on the reflective electrode 214.
Since the change of the optical properties (change of polarization coefficient) of a liquid crystal occurs by the potential difference between the reflective electrode 214 and the liquid crystal common electrode 216, by controlling the potential of the reflective electrode 214 of each pixel, an image is formed.